Sage Publications, Inc, 2006
Majalah, Jurnal, Buletin
Plamenatz, John
Longmen Press, 1993
Buku Teks
Plamenatz, John
Longman Press, 1992
Buku Teks
David Boucher, Paul Kelly, editor
Oxford Univesity Press, 2009
Buku Teks
Paige, Glenn D., author
University of Hawai, 1993
Buku Teks